Process of separating intermixed divided materials



2 sheets-sheet 1 May 9, 1944- c. w. H. HOLMES PROCESS OF SEPARA'IYINGINTERMIXED DIVIDED MATERIALS Filed Nov. 25, 194;

' INVENTOR ATT NEY y, 1944- c. w. H. HOLMES 2,348,344

PROCESS OF smmme INTERMIXED mvxpnn MATERIALS Filed Nov. 25. 1941' 2Sheets-Sheet 2 INVENTOR 1 4 16 Mew; 720-7144.,

Patente d May 9, 1944 PROCESS OF SEPARATING INTERMIXED DIVIDED MATERIALSColin William Higham Holmes, Durham City,

England, assignor to The Birtley Company Lim itecl, Birtley, EnglandApplication November 25, 1941, Serial No. 420,337

1 Claim. (Cl. 209-467) This invention relates to the separation ofsubstantially dry, intermixed, divided materials whose constituentparticles differ in density.

In general, theinvention will be described with reference to theseparation of slate or other refuse from coal, but it will be understoodthat neither the process nor apparatus is confined thereto.

Objects and advantages of the invention will be set forth in parthereinafter and in part will be obvious herefrom, or may be learned bypractice with the invention, the same being realized and attained bymeans of the steps, instrumentalities and combinations pointed out inthe appended claims.

The accompanying drawings, referred to herein and constituting a parthereof, illustrate one embodiment of apparatus for carrying out theinvention, and together with the description, serve to explain theprinciples of the invention.

Of the drawings:

Fig. 1 is a top plan view of a twin deck separator on which the improvedprocess may be carried out;

Fig. 2 is a vertical longitudinal section on line 22 of Fig. 1;

Fig. 3 is an enlarged transverse vertical section on line 33 of Fig. 2;

Fig. 4 is a transverse section on line i--4 of Fig. 2; and

Fig. 5 is a diagrammatic longitudinal section of a modified form of deckillustrating the operation of the invention on a bed of intermixed coaland refuse materials.

The invention is directed to providing an improved process forseparation of such intermixed divided materials according to theirdifferences uct and also without the necessity for removing a so-calledmiddlings product which is commonly required in other types ofseparating processes without sacrificing the purity of either the coalor the refuse products.

One object of the invention lies in the provision of a combination ofmechanical and pneumatic means, whereby both the efiicient separation ofthe raw material and the discharge of the separated products is renderedsubstantially automatic and therefore independent of (1) fluctuations inthe feed quantity of raw material from zero up to a predeterminedmaximum, and (2) substantially independent of variations in the relativeamounts of light and heavy particles, or, alternatively, of coarse andfine particles, or both, in the raw feed.

As to process improvements the invention primarily relates to that typeof pneumatic separating operation wherein the raw materials are fed tothe surface of an inclined, reciprocating, air-pervious deck where theyundergo pneumatic stratification and the separating action andreciprocating movement are such that the upper strata-of coal or lightermaterial travel downwardly to discharge at the lower end of the inclineddeck, while the inferior strata heavy material travel upwardly in theopposite direction to discharge at the upper end of the inclined deck.The improved process features primarily responsible for the improvedseparating action of the invention comprise generally the provision of apervious deck or separating surface that is horizontal at right anglesto the reciprocating or head motion but which is more steeply inclinedto the horizontal towards the discharge of the heavy particles than it'is towards the discharge of the light particles.

Cooperating with the aforesaid deck, the invention provides for themaintenance and control of a critical air pressure condition which is sorelated to the resistance of the air pervious deck that suitable andunique separating conditions are maintained at all times regardless ofchanges in the quantity and character of the raw feed. For this purposethe invention provides a supply of air under pressure, control valves,an air chamber below the deck or separating surface, the said separatingsurface being relatively smooth on its upper surface and so designedthat it diffuses and restricts the volume of air which escapes throughits perforate surface by virtue of the pressure maintained within theair chest, the said restriction lying between two relatively closevalues.

For carrying out the aforesaid process improvements, the invention alsoprovides certain improved mechanical means. One such improvementconsists in the conversion of the smooth rotary'motion of the drivinghead shaft into a reciprocating motion at the deck or separatingsurface, the said motion being'at a substantially greater angle to thehorizontal than those between the separating surfaces and thehorizontal, the motion being characterised by the fact that it is freefrom sudden drops or jolts.

Another object of the invention lies in the provision of means wherebythe horizontal component of the reciprocating motion is substantiallyabsorbed by a system of levers and torsion spring bars in the downwardand backward stroke, and this energy is returned by the springs to thereciprocating mass during the forward and upward stroke, so that therelatively large and heavy masses involved in the separation of largequantities of raw material may be reciprocated, by way of example,through 1200 reversals per minute with an amplitude of without creatingclearances in the driving head or link joints or other parts of themechanism and without creating destructive secondary vibrations eitherat the separating surface or in the supporting structure,

so that a continuously uniform mechanical agita tion can be transmittedto the bed of particles as a whole and so that acontinuously uniformtraverse effect can be transmitted to the stratified heavier componentof the mass. In this connectior the present invention eliminates allauxiliary fittings such as deflecting riflie s, overlays, and the like,to augment the traverse eifect of the head motion whose influence on theseparation varies as they become worn, and also eliminates vanesorbaflies placed aboveor below the pervious deck for the deflection ofcurrents of air.

} Anfimportant difierence between the present invention and thegpriorart lies in thefa'ct that prior machines acted much as jiggingconveyors,

operating continuously in removing the lower stratum of the bedirrespective of its'composition, whereas in the case of the processdescribed herein the constant traverse value is always present, but itonly effects a removal of the lower stratum when said stratum is in asubstantially pure condition and when its accumulation has createdcertain pneumatic and thrust conditions in the zontal at its lower endto a steeper inclination at its upper end, because it has been found byexperiment that substantial automatic operation cannot be obtainedand'continuously maintained on a plane surface;

It has also been found by experiment that said combination of deckanglesis necessary(l)' to permit of the free flow of the stream of lightparticles off the lower end'of the deck, and at the same time to permitof' the retention of a bed of light particles of predetermined depthwhen the raw feed stops; (2) to permit of the formation of a relativelyfluid reservoir of heavy particles having a head value that is to allintents and purposes hydraulic in its action, so that heavy particlesare not discharged underno-load conditions but are (to use an analogy)pumped away by the head motion so soon as the accumulation of furtherquantities of stratified heavy particles 7 create the necessarypneumatic and thrust conditions forthe head motion to take eifect;

It has also beenfound by. experiment that both the value of the angle ofthe slope down which the light particles flow off the deck and the valueof the difference between this angle and that up which the heavyparticles are traversed are criticaLthedifierences of theorder of plusor minus usually necessary in the treatment of the finest one degreebeing important in any given set of circumstances.

Further, it has been found by experiment that if the pervious deck iscontinuous inclined plane, the conditions under which separation can beobtained are too critical to give automatic operation, while on theother hand if the diiference between the slopes of the two ends of thedeck is too great the heavy particles will accumulate on its surfaceuntil they have damped out the desired pneumatic condition over a largearea, after which the whole bed of particles will discharge rapidly atthe upper end of the separator and the separation will then gopermanently out of balance.

' Machines constructed according to the prior art were generallyprovided with decks of high air permeability; for example being deckedwith woven wire cloth, that is to say, with a cover having not less than25% of its area available for the escapement of air from the underside.Alternatively, the air-pervious deck cover consisted of a perforatedmetal plate having a relatively high percentage opening, for example,between 25% and 40% of the plate area. Because of this fact such priormachines usually employed baffles or deflecting vanes beneath the decksurface so as to direct and control the distribution of the air blastpassing upwardly through the deck.

In the process as carried out in accordance with the present invention,the air-pervious deck cover is so constructed as to oiTer a greaterresistance to the passage of air than was the case in the prior art, forexample, deck covers with an effective opening of less than 2% of theplate area are of escapement of the air is rendered uniform over thewhole deck area when empty without the use of deflecting vanes, or thelike, although a greater degree of restriction than this limiting valueis usually employed.

Apart from acting as a diffuser, the restriction imposed by the decksurface upon the escapement .of air through it must be sufficient tocreate a pressure condition in the air chest greater than that requiredto break down the maximum thickness of coal bed to a fluid condition andto maintain the bed in this state while permitting only a relativelysmall variation in the volume of air passing through the bed as itsresistance varies from full load to no-load conditions, or,alternatively as its resistance increases or decreases due to size ordensity segregation in the raw feed.

In carrying out the separation of refuse from coal, by way of example,on pneumatic separators having a deck shaped and mounted as shown in.the accompanying drawings, three different conditions have beenobserved as a result of experi- ,ment with changes in the air-pressureconditions,

as follows:

(1) With machines decked according to the prior art, that is to say,with a ratio of opening to deck area of approximately 1:4, it is foundthat slight variations in the rate and/or grading and/or refuse contentof the raw coal feed will, by way of example, cause the resistance ofthe bed to fall at the lower end of the separator where it is covered byabed of clean coal particles.

When this happens, the deck-' offering relatively little resistance tothe passage of the air- -permits of a prompt and greatly increasedescapement of air, with the result that the pressure condition in theair chest falls and (with a given air-fan'output) is no longersufficient to maintain the bed of refuse (which occupies 30-50% of thedeck area) in a reasonably fluid condition, so that partly by virtue ofthe increased proportion of its mass that registers on the deck surface,and partly due to the fact that friction between the deck and thelowermost layer of refuse particles as well as that between theindividual particles themselves is increased, the whole bed, includingthe overlying coal; takes the traverse of the head motion and is rapidlydischarged at the upper end of the deck surface.

It will be understood that so long as the lower end of the deck is freeto vent air against a low resistance, the separation will not recoverandthe separator will continue to act as a jigging conveyor, dischargingthe whole of the feed at the upper or refuse discharge end.

(2) With similar machines and raw coal feed, but with a deck cover, forexample, with a ratio of opening to deck area of 1:10, similarconditions obtain though not to the same degree. The discharge of refusewill be intermittent, occurring at an abnormal rate for a few seconds,after which the fringe of the refuse bed will recede from the refusespillage edge of the separator and the whole refuse bed will then slipdown the deck towards, and sometimes over, the clean coal spillage edge,leaving the upper end of the deck surface exposed. This gives arelatively free vent to the air at the upper end of the deck, which, inturn, causes a slightly reduced pressure beneath the bed of refuse; inconsequence it again takes the traverse of the head motion and gives abrief and abnormally heavy discharge before ble.

(3) With a similar machine and raw coal feed,

but with a deck cover, for example, with a ratioof opening to deck areaof 1:20, that is to say, in accordance with the present invention, ithas been found by experiment that the separation will remaincontinuously in balance despite any fluctuations in the rate of feedbetween zero and maximum and irrespective of any variations that have sofar been observed as regards the grading of refuse content of the rawcoal feed.

It is found that under these conditions any reduction in the rate offeed causes, of necessity, a reduction in the depth of the stream ofclean coal flowing downwardly over the incl ned lower end of theseparator deck, with theresult that the resistance of this bed to thepassage of air is decreased. I

But the resistancev of the bed of coal is no longer the main controllingfactor. It is now the deck, and the restriction that it offers 15 sogreat that although it will transmit suflicient pneumatic energy tomaintain the bed in a fluid the separator.

and free stratifying condition it will not pass a sufficient excess ofair with a bed of lower resistance either to blow the bed off the deckaltogether or to permit of a damaging reduction in pressure beneath thatportion ofthe deck which supports the bed of refuse.

In consequence, the refuse bedon the more steeply inclinedpart of thedeck is maintained in a su-iiiciently fluid condition for it to maintainits hydraulic head effect on the refuse lying on the flatter portion ofthe deck and also in such a fluid state that it is not affected by thetraversing influence of the head motion. Thus under no-load conditionsthe bed remains stationary,

that is to say, that it does not travel up or down the inclined surfaceand neither clean coal nor refuse is discharged, although the headmotion is being imparted to the deck.

If pro-cleaned coal is now substituted for the raw feed, it is alldischarged at the lower or clean coal discharge end of the deck, and ifrefuse is fed to the machine it stratifles below the clean coal on thedeck surface slightly increasing the length and depth of the lower endof the refuse bed on the separator.

As the refuse bed under no-load conditions is in balance with thecombined mechanical and pneumatic forces, tending respectively to causeit to discharge at the upper end of the deck or to slip back down theinclined supporting surface, the addition of this further refuse and theconsequent extension of the refuse bed on to the flatter portion of thedeck upsets this balance because:

(a) A portion of the refuse bed now rests on an area of the deck whichis flatter than the angle of slip under the uniform pneumatic conditionsthat have been constructed, the head mo tion therefore traverses ittowards the refuse discharge end of the separator, with the result thatit displaces an equivalent amount of the balanced refuse bed over thedischarge edge of the separator.

(b) In effecting this, the previously balanced refuse bed must becomeslightly deeper before it can discharge overthe shal spillage edge, andthis again has a slight pneumatic effect in increasing its traverseaction.

It will be understood that thebed of refuse is in equilibrium until anadditional thrust value is imposed upon it by freshly stratifled refuse,and, further, that such thrust must. be transmitted throughout thelength of the refuse bed so as to permit of the discharge of refuse fromIt will also be understood that such transmission of energy can only beeffected over a relatively smooth deck surface, and that any teeth,steps, overlays or other obstructions on the deck surface such a wereemployed in the prior art in order to traverse out the refuse, would,with the present invention, interfere with the smooth and practicallyhydraulic transference thatis obtained by the process as describedherein.

' It will also be understood'that an essential discovery of thisinvention lies in the maintenance of a reserve of pneumatic energy inthe form of a pressure condition beneath the pervious deck incombination with means for limiting the rate at which this reserve ofenergy in the form of pressure can be dissipated in velocity form,thereby ensuring that the pneumatic conditions under which thestratification of the raw product and the removal\ of theseparatedproducts shall not vary except between such narrow limits as to permitof prompt and continuous stratification and separation irrespective ofsuch fluctuations in the quantity and quality of the feed as arecommonly met with in the art.

It will also be understood that the invention is not confined to the useof a deck cover having a permeability ratio of 1:20. It hasbeen found byexperiment, for example in the separation of coal from refuse that:

(1) The maximum percentage opening in the deck cover necessary tostabilise the separation is a function of the square root of thediameter of the largest particle.

(2) When round openings are employed their diameters should preferablylie between mm.

and 1 mm., depending upon the size of material to be separated.

(3) The distributions of the perforation should be reasonably uniform.

It will be understood that the foregoing general description and thefollowing detailed description as well are exemplary and illustrative ofthe invention but are not descriptive thereof.

Referring now in detail to the present preferred embodiment of theinvention illustrated by way of example in the accompanying drawings,the invention provides an air pervious deck I as hereinabove described,which deck together with an air chest or air chamber 2 mounted beneathit and fixed to it, is adapted to be reciprocated longitudinally upon astationary supporting frame 3.. The air chest is flexibly connected to afan or other source of pressure air by means of one or more evass 6. The

reciprocatory motion of the deck and air chest with respect to the frameis made possible by links I pivotally mounted at their lower ends inrubber bushings carried by the frame 3 and connected at their upper endsthrough similar bushings to the under surface of the air chest 2.

Mechanical energy from any suitable source is transmitted to themechanism through a suitable pulley I 0, mounted upon a shaft II,supported in ball bearing blocks I2, and upon which are mounted ballbearing eccentrics I3, the whole being mounted in a casing I4.

The eccentric motion is transmitted to the separator by means ofeccentric rods I5, terminating in rubber bush fittings I6, the line ofsaid motion being such that it passes through, or as nearly as possiblethrough, the center of gravity of the reciprocating mass.

Torsion spring bars I! are rigidly connected to the air chest structure2 at their inner ends. They are fixed in pairs coaxially with thecenters of oscillation at the upper ends of the supporting links, andtheir outer ends are rigidly connected to the upper ends of levers 9,which terminate at their ends in slots running radially with theclamping bolts I8 in the lower ends of the supporting links.

In order to set up this torsion spring balancing arrangement, bolts I8are slackened and the eccentric shaft is rotated, until the air chest isnearly at the end of the forward and upward stroke. Bolts l8 are thentightened up so that the levers 9 are fixed rigidly to the inner linksI, the contacting surfaces being roughened so as to eliminate thepossibility of slipping. The

mechanism will then settle down so that it is almost on the bottom andrearward center, thus placing a torsional stress on the spring bars II.In actual operation these bars are stressed duringeach cycle and theenergy stored in them is released during the forward and upward stroke,thus eliminating reversal shocks in the mechanism generally, and moreespecially reversals of stress in the eccentric rods I5.

Means are provided for maintaining a suitable and preferably substantialdepth of bed of materials on the deck under no-load conditions. For thispurpose the raw material to be treated is fed uniformly across the widthof the separator along a line at right angles to the head motion, andapproximately one-third of the length of the deck away from the refusedischarge. The source of feed may be a surge bunker, although, providedthat the rate of feed does not exceed a predetermined maximum, the rawmaterial may be handled in stream and the surge bunker eliminated.

Adjustable spillage edges 4 and 5 are provided at the upper and lowerends respectively of the deck so that the depth of the bed under no-loadconditions can be set to any desired value.

Referring now to Fig. 5, the distribution of the refuse and coalparticles is diagrammatically shown upon the pervious deck under noloadconditions. and at the instant of recommencing the feed. It will beunderstood that this drawing is purely diagrammatic and that it is notto scale. It will be seen that the bed of refuse particles on the moresteeply inclined portion of the deck terminates in a shorter length ofbed resting on the flatter portion of the deck and whose length is shownby the dimension X. It will be understood that on feeding further rawmaterial to the separator, this is promptly stratified and the heavierparticles sinking to the deck surface give a length of bed greater thanX, and, in consequence, have a greater thrust value towards the spillageedge 4 than previously. In consequence, refuse is dischargedcontinuously until such times as the length of refuse bed on the flatterportion of the desk returns to the length X, when conditions are againbalanced.

The lighter coal particles stratifying above the refuse are maintainedin fluid bed form by the air pressure in combination with thereciprocating motion, and flow in stream form continuously down theangle a over the spillage edge 5.

Means are provided for altering both angles a and b simultaneously byadjusting the slotted fixings l9 and 20 in Fig. 2, and either angle canbe altered independently by loosening, adjusting and reclamping the twoor more sections of the deck between the upstanding walls of the airchest.

As shown by way of example in Fig. 2, the air pervious deck I is formedas three panels wherein the intermediate panel is fixed, while the loweror forward panel I a is pivoted at 2| to vary the slope of said panelwith respect to the intermediate section I (which conforms generallytothe area marked X in Fig. 5), while the upper or rearmost panel lb ispivotally connected to panel I at 22 thereby to be positioned to formthe steeper angle b as diagrammatically indicated in Fig. 5. Themounting of the panel is with respect to the deck frame 25 and theintermediate dividing wall 26 will be clear from Fig. 3. The inventionis exemplarily shown as applied to a double or twin deck constructionwherein one-half of the deck may be operated independently of the otherhalf and upon materials having different characteristics, if desired,and the construction thereby permits of setting the various deck panelsat different angles as regards the operations of the two side-by-sidedecks.

It will be understood that the deck may be formed as shown in Fig. 5,that is, with two fixed slopes corresponding to the anglesa and b orthat a number of variably positionable panels similar to those in Fig. 2may be used in greater number so as to vary the angularity of differentparts of the deck at different ratios, without departing from the spiritof the invention.

It will also be understood that presized or substantially unsized coalmay be treated, that either one or both of the products from thepreliminary separation may be subject to screening and subsequentretreatment, or to retreatment without such screening, and that theprocess and apparatus may be employed in the cleaning of coal or in theseparation of other substantially dry and divided materials inconjunction with other processes and apparatus known in the art.

7 As has been previously stated, the permeability of the deck I will inall cases be so restricted as to set up the air-pressure conditionhereinabove described. It will be understood that the showing of an airpervious deck in the drawings hereof is entirely diagrammatic and is notintended to be representative of the actual ratio of air permeability.

It will be understood also that the decks may be constructed ofcup-punched plate instead of plain punched plate, in order to obtain amore efficient transformation of the pressure condition beneath the deckinto the velocity condition above it; the ratio of the height of thecupping to its diameter being of the order of 1:4, the deck surface isstill maintaining in a smooth condition, and it has been found byexperiment that roughening to this extent does not interfere with theseparation according to the present invention.

Also it will be understood that when the separating surface consists oftwo or more parallel channels divided by upstanding walls, as shown,that each of said channels may be equipped with decks having differentpercentage openings and/or different inclinations and/or differentdepths of bed, and that they may operate with different air pressures sothat two or more different qualities or sizes of coal may be separatedsimultaneously on a single machine.

The invention in its broader aspects is not limited to the specificmechanisms shown and described but departures may be made therefromWithin the scope of the accompanying claim without departing from theprinciples of the invention and without sacrificing its chiefadvantages.

What is claimed is:

The process of separating intermixed divided materials which comprisesfeeding said materials to an inclined air-pervious surface between theends thereof, imparting a reciprocating head motion to said surface toimpel materials toward the upper end thereof, passing air underpredetermined pressure upwardly through said surface and the bed ofmaterials formed thereon to stratify and fluidize said materials,causing lighter materials to travel downwardly longitudinally to thelower end of the surface to discharge by inclining the surface at apredetermined angle between the feed-on point and the lower end of saidsurface, opposing the opposite upward travel of heavier materials byinclining the surface at a greater angle between the feed-on point andthe upper end of said surface causing stratified heavier materials todischarge at the upper end of said surface and maintaining the airescapement through the bed substantially constant under changes in theair resistance of the bed of materials by providing throughout thesurface an airpermeability which is relatively low compared to that ofthe bed under maximum load conditions, and by maintaining a substantialair pressure beneath said surface, and constraining all materials todischarge at the ends of the surface by preventing lateral movement andescape thereof.

C. W. H. HOLMES.

